1. Field of the Invention
This invention relates to a micrometer. Particularly, it relates to a micrometer which is designed to reduce the cost and weight.
2. Description of the Related Art
As shown in FIG. 10, a micrometer comprises an almost U-shaped main body 101, an anvil 102 held at an end portion of the main body 101, a spindle 104 screwed into the other end portion of the main body 101 through an inner sleeve 103 to move toward and away from the anvil 102, an outer sleeve 105 placed and fixed onto the outside of the inner sleeve 103, a thimble 106 rotatably covered on the outside of the outer sleeve 105 and integrally connected with the spindle 104, and a ratchet mechanism 107 which slips when an excess load is applied on the spindle 104, and is provided at the rear end of the spindle 104.
On the outer circumferential surface of the outer sleeve 105, a graduation 108 of a main scale is formed at a predetermined pitch along the axial direction, and on the outer circumferential surface of the thimble 106, a graduation 109 of a vernier scale is formed at a predetermined pitch along the circumferential direction. By these graduations 108, 109, the amount of displacement of the spindle 104 to the anvil 102 can be measured. In other words, dimensions of the object which is held between the anvil 102 and the spindle 104 can be measured.
However, since the main body 101 of the conventional micrometer is molded by casting, there is a disadvantage that the production costs are high. The processes of producing the main body comprise following steps of: making a mold having a cavity which is equivalent in size and shape as that of the main body; pouring a molten sintered alloy or ductile iron (FCD400) into the cavity; taking out the casting from the split mold after cooling the molten metal; sintering the casting; removing the burrs on the casting; and boring holes on the casting to press fit the anvil 102 and the inner sleeve 103. Therefore it needs much expense in time, effort and cost.
In addition, such castings being heavy in weight, it also brings up a disadvantage of spoiling the handling properties and operability, when it is used as a micrometer which performs measuring while holding it in one hand.
Besides, when the measurement is carried out with supporting a part of the main body 101 by hand, the heat of hand is directly transferred to the main body 101, resulting in the thermal expansion of the main body 101. Therefore the measures to get rid of the influence become necessary. Conventionally, as one of the measures for this point, a cover 110 has been attached with screws on the portion of the main body 101 where it is gripped by hand. However, it results in, not only an increase in weight and size but also the increase in time and labor for the attachment and cost of it.
It is an object of the present invention to provide a micrometer which enables it to reduce the cost and the size.
It is another object of the present invention to provide a micrometer which can restrain the influence of thermal expansion caused by the heat of hand.